Primer composition of nitromethane, polymeric foam, and hollow spheres

ABSTRACT

A primer adapted to initiating detonation of nitromethane by strong shock comprising an open-celled polymeric foam containing about 15-85 percent by weight of glass bubbles.

United States Patent Chandler 1 1 Sept. 2, 1975 1 PRIMER COMPOSITION OF156] References Cited NITROMETHANE, POLYMERIC FOAM. UNITED STATESPATENTS AND HOLLOW SPHERES 3.697.668 10/1972 Campbell 149/2 X Inventor:0. Wayne Chandler, Terre Hnute.

Assignee: Commercial Solvents Corporation,

Terre Haute. 1nd.

Filed: Aug. 16, 1973 Appl. No: 388,872

Related U.S. Application Data Division of Ser. No. 333.845. Feb. 20,1973.

U.S. C1. 149/2; 149/194; 149/89;

Int. Cl C06b 19/00 Field of Search 149/2. 21. 89. 90. 97.

Primary Etaminer-Stephen .1. Lechert. Jr. Attorney, Agent, 0" FirmRobertH. Dewey; Howard E. Post 6 Claims, No Drawings PRIMER COMPOSITION OFNI'IROME'IHANE.

POLYMERIC FOAM. AND HOLLOW SPHERES This is a division. of applicationSer. No. 333.845. filed Feb. 20. 1973.

BACKGROUND OF THE. lNVEN'llON This invention relates to an explosivecombination. In a particular aspect this invention relates to a primeradapted to initiating detonation of nitromethane by strong shock.

Nitromethane is a very stable liquid but it can be detonated underextraordinary conditions. When it does detonate. it is extremelypowerful and is useful in many special applications. However thedifficulty in initiating detonation has long been a problem. oftenrequiring expensive primers and boosters.

It is known from Minnick. US. Pat. No. 3.338.165 that insolubleair-entrapping materials. such as resin balloons. can be uniformlysuspended in gelled nitromethane and thereby render it sensitive todetonation by strong shock. It is necessary to gel the nitromethanebecause otherwise the air-entrapping material will segregate whereuponthe composition loses its sensitivity to strong shock and does notdetonate when the initiator is fired.

The compositions disclosed by Minnick are satisfactory when freshlyprepared but they suffer from several disadvantages. For field use. itis inconvenient. if not impossible. to gel the nitromethane at the siteof use and uniformly mix in the air-entrapping material. It is possibleto prepare the composition ahead of time and transport it to the site.but it has been found that the composition loses its sensitivity onaging. possibly due to displacement of the entrapped air bynitromethane. Also it is risky to transport a shock-sensitive explosivemixture under field concitions. Furthermore. once the composition hasbeen prepared. it cannot be easily dcsensitized if it is not usedpromptly.

Accordingly, there is a need for an improved method for detonatingnitromethane.

SUMMARY OF THE INVENTION It is an object of this invention to provide anexplosive composition.

It is another object of this invention to provide a primer adapted toinitiating detonation of nitromethane by strong shock.

Other objects of this invention will be apparent to those skilled in theart from the description herein.

It is the discovery of this invention that a combination of anopen-celled polymeric foam having microspheres of entrapped airdispersed therein. including embedded on the surface thereof. and placedin intimate contact with nitromethane provides an explosive systemsensitive to strong shock by detonation. The foam having themicrospheres dispersed therein comprises a primer for detonatingnitromethane and provides a method for priming nitromethane todetonation by strong shock to which it would otherwise be stable.

DETAILED DESCRIPTION According to the present invention. whennitromethane is to be detonated. the polymeric foam containingmicrospheres of entrapped air is placed in intimate contact with asuitable shock-producing device. e.g. an electric blasting cap. The capand foam is then placed in intimate contact with the nitromethane, eg byimmcrsion. or by placing in a capwell or tube and then immersing. Whenthe cap is fired. it results in detonation of the nitromethane.

The primer of the present invention is particularly advantageous becausethe nitromethane remains highly stable until the primer is immersedtherein: Furthermore. the primer can be easily removed prior todetonation if desired. The primer is also easily produced.

The microspheres of entrapped air suitable for the practice ofthisinvention can be the resin balloons. i.e.. phenol-formaldehyde orurear-formaldehyde. as described by Minnick in US. Pat. No. 3.338.l65which is incorporated herein by reference thereto. Preferably however.the microspheres are made of glass. ceramic or other materialsimpermeable to nitromethane. Suitable grades are commercially availablefrom. e.g. 3M Corporation. Minneapolis. Minnesota. and Emerson- CumingCorporation. Canton. Massachusetts.

The polymeric foam can be any open-celled foam which is impermeable tonitromethane. Polyethylene foam is unsatisfactory. as is foamedcarborundum ceramic foam (which is not a polymeric substance. ofcourse). The preferred polymeric substance is a polyurethane foam.

The polyurethane foam suitable for the practice of this invention ispreferably an open-celled foam having a density of about 0.02 to about0.04 g/cc. The foam density is primarily controlled by the volume offrothing agent used in making the foam. The term opencelled-- isintended to mean that the walls of some of the cells are discontinuousso that a portion. but not all. of the air entrapped therein can bereplaced by liquid when the foam is immersed in a liquid. The closedcells constitute microspheres so that. to a limited extent. the foamitself can serve as the primer of the present invention. However it isnot reliably so. because attempts to detonate nitromethane with the foamalone frequently fail. The polymeric foam itself is not therefore asatisfactory primer.

The preferred primer comprises an open-celled polyurethane foamcontaining l585 percent of glass or ceramic microspheres. preferably30-85 percent. The primer can be conveniently prepared by mixing aliquid monomer. or mixture thereof. with the microspheres at aconcentration of about 15-85 percent by weight. The foaming agent andcatalyst are then added. the mixture is heated and the foam withmicrospheres more or less uniformly dispersed therein is therebyproduced. The production of polymeric foams is well-known in the art andit is not intended that the invention be limited to any particularmethod or formulation.

Another convenient and preferred method of preparing the primer is toshake or tumble relatively thin pieces or shreds of the foam with themicrospheres. which thereby become embedded. or enmeshed. in the foam atthe surface. When the combination is so prepared it may contain as muchas 85 percent by weight of microspheres at a surface density of about0.5 g. microspheres per square inch.

In use. a portion of about l3 cubic inches of the polymeric foam withmicrospheres is attached to a detonating device, e.g. a detonating cordor a blasting cap, e.g. by threading it on the cap; or it can be packedinto an aluminum tube or a c apwell. then the cap or detonating cord isinserted. When the cap or cord is fired. the nitromethane detonates.

The invention will be better understood with reference to the followingexamples. It is understood. however, that the examples are intended forillustration only and it is not intended that the invention be limitedthereby.

EXAMPLE 1 A polyurethane foam containing glass bubbles was prepared bythoroughly mixing the following materials:

Pol \ol 100 g Water 3 Stannous Octoatc l Blowing Agent l Bubble si/econtroller 2 Toluene diisocyanate 38.3 (ilass bubbles 25 Total 179.3

The mixture was then placed in a 300F oven for about minutes therebyproducing the polyurethane foam having glass bubbles dispersed therein.

The polyol used was a trio] having a molecular weight of 3500 and ahydroxyl number of 3514. It is marketed by Jefferson Chemical under thedesignation Thanol F-35 14.

The blowing agent used was a liquid mixture of fluoro-chloroalkanesmarketed by Union Carbide Corporation under the designation Propellant ll.

The bubble-size controller was a silicone surfactant marketed byDow-Corning Corporation under the designation DC-l93.

The glass bubbles are marketed by 3l 1 Corporation under the designationB-40-B. These bubbles are described as having an average true particledensity between 0.30 and 0.40 g/cc and bulk density of about 0.23/cc.The size of the particles is between and 100 microns.

In the above formula, the 3 g of water reacts to form 7.3 g of carbondioxide and the propellant is volatile. The total weight of the glassbubbles and the foamed polyurethane is therefore 169.3 g. The percentageof weight of glass bubbles was about 15 percent. The density of the foamwas 0.0246 g/cc.

About 3 oz. of commercial-grade nitromethane was transferred to a 4-02.paper cup. A one-inch cube of the polyurethane foam was pierced with asharp object and a No. 8 electric blasting cap was inserted therein. Thecap and foam were then immersed in the nitromethane, and the foam wassqueezed lightly to insure wetting the foam with nitromethane. When thecap was fired, the nitromethane detonated. The test was repeated fourmore times with identical results. When the foam was not used. thenitromethane did not detonate.

The test was repeated in all essential details except that the glassbubbles were omitted. ln five tests with the foam only, unsatisfactorypartial detonations were obtained each time.

EXAMPLE 2 A polyurethane foam containing glass bubbles was prepared asfollows:

Polyol F- l4 I00 g Water 'l'ricthylencdiaminc 6 Bubble size controller 7-Continued Dimeth lalninoethanol 2 Methylene chloride 25 (ilass Bubbles30 Total l 3 In the above formula. the methylene chloride is volatileand did not become a permanent part of the foam. The percentage byweight of glass bubbles based on the foam was 2 l .3 percent. Thedensity was not measured, but the foam was open celled. comparable tothat of Example l.

A l-inch cube of foam was pierced and a No. 8 blasting cap was insertedtherein. The cap and foam were immersed in about 3 oz. of nitromethaneand the foam was squeezed lightly to insure wetting of the foam with thenitromethane. The nitromethane detonated when the cap was fired. Thetest was repeated two more times with identical results. In three trialswith nitromethane without the foam, the nitromethane failed to detonate.

The test was repeated in all essential details except that the glassbubbles were eliminated. In three trials with the foam alone, containingno glass bubbles, the nitromethane detonated partially in two and failedto detonate in the third.

EXAMPLE 3 The experiment of example 1 was repeated in all essentialdetails except that 30 g of glass bubbles were used in place of 25 g.The percentage in the foam was 17.2 percent. It was observed that thefoam was not of uniform quality throughout and the results of detonationtests reflected the inconsistency.

The tests were conducted using 18-02. samples of commercial gradenitromethane containing a minimum of percent by weight nitromethane. Ablock of foam, usually 1 X 1 X 2,inches but in a few tests 2 X 2 X 8inches, was immersed in nitromethane and squeezed lightly. It was theninserted in the eapwell and a blasting cap was inserted in the capwell,which was then immersed in the nitromethane.

The first test using an Atlas (A) 16 cap and a l X l X 2-inch block offoam failed.

In the second and third tests using a 2 X 2 X 8-inch block of foam froma different batch than the first, the nitromethane failed to detonatewith a duPont (D) 6 and an A-] 0 cap.

In a fourth and fifth test using a l X l X 2-inch block of foam from thesame batch as the second and third tests, the nitromethane failed todetonate with an A-8 cap, but did detonate with an A-l6 cap.

In tests 6, 7, and 8, a l X 1 X 2inch block of foam from a third batchwas threaded onto a cap which was then immersed in the nitromethane. andsqueezed lightly. In the sixth test using an A-6 cap. the nitromethanefailed to detonate, but in tests 7 and 8 using a D-6 and an A-l0 caprespectively. detonations occurred.

The foregoing experiment was repeated in all essential details exceptthat the glass bubbles were eliminated from the foam.

In the first test, the nitromethane failed to detonate using an A-l0 capbut did detonate with an A-l6 cap. In the second test, using foam from adifferent batch than the first, the nitromethane failed to detonate witha D-6 cap, but detonated with an A-l0 cap. In the fourth test thenitromethane failed to detonate with an A-8 cap, but did detonate withan A-l6 cap. in tests 6.

7 and 8. using foam from yet a different batch than either of theforegoing. the nitromethane failed using a D-6 and an A-S cap. butdetonated with an A-l cap.

EXAMPLE 4 A sheet of commercially-available. open-celled polyurethanefoam. /2 inch thick. was obtained on the open market and was cut into 1A X 3-inch pieces. weighing about 1.2 g each. and having a total surfacearea of about 13.5 inches. The density was 0.032 g/ml. Each piece wasshaken with ceramic microspheres unitl it was determined that a maximumamount had been embedded in foam. About 7 g was so embedded on thesurface of the foam. giving a composition containing about 85 percentmicrospheres at a surface density about 0.5 g/in A piece of foam sotreated was inserted into a thinwalled aluminum tube. closed by crimpingat one end. of the type used for toothpaste etc. An Atlas No. 16blasting cap was inserted therein and the assembly was immersed innitromethane. When the cap was fired. the nitromethane detonated.

The experiment was repeated in all essential details except that insteadof shaking the foam with the microspheres an adhesive was used to securethem to the foam. The nitromethane failed to detonate.

EXAMPLE The experiment of example 4 was repeated in all essentialdetails except that an Atlas No. l0 cap was used. When it was fired. thenitromethane detonated.

EXAMPLE 6 The experiment of example 4 was repeated in all essentialdetails except that 100 grain pentaerythritol tetranitrate detonatorcord was substituted for the blasting cap. When the cord was tired thenitromethane detonated. The experiment was repeated using 60 grain cord.The nitromethane detonated.

EXAMPLE 7 The experiment of example 4 was repeated in all essentialdetails except that shredded polyurethane foam sold commercially forpillow stuffing was substituted for the sheet foam. The shreds wereabout 0.5 X 0.5 X 0.5 inches and about 1.2 g was used per test. As inexample 8. about 7 g of microspheres were embedded in the surface of thefoam. When the combination was used with an Atlas No. 16 or No. 10blasting cap. or with 100 grain or 60 grain detonator cord. detonationsof nitromethane occurred without fail.

I claim:

1. A primer adapted to initiating detonation of nitromethane by strongshock consisting essentially of the combination of an open-celledpolymeric foam having dispersed therein from about [5 to about percentby weight of hollow thin-walled microspheres containing entrapped airsaid foam being in intimate contact with nitromethane.

2. The combination of claim 1 wherein said polymeric foam ispolyurethane having a density of from about 0.02 to about 0.04 g/ml.

3. The combination of claim 1 wherein said microspheres are ofphenol-formaldehydc. ureaformaldehyde. glass or ceramic.

4. The combination of claim 3 wherein said microspheres are glassbubbles of about 20 to microns and have a true particle density between0.3 and 0.4 g/cc.

5. The combination of claim 1 wherein said microspheres are dispersedthroughout the polymeric foam including the surface.

6. The combination of claim I wherein said microspheres are embedded atthe surface of said polymeric foam.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 902,933D t d September 2 1975 0. Wayne Chandler Inventor(s) It is certifiedthat error appears in the above-identified patent and that said LettersPatent are hereby corrected as shown below:

Column 3'; line 35, "311 Corporation" should read 3M Corporation Columnline 11, "unitl'" should read until Signed and Scaled this SeventeenthDay 0f May 1977 [SEAL] RUTH C. MASON C. MARSHALL DANN Arresting OfficerCommissioner uflatems and Trademarks UNITED STATES PATENT OFFICECERTIFICATE OF CORRECTION Patent No. 902 Dated pt m 2 1 7 0, WayneChandler Inventor(s) It is certified that error appears in theabove-identified patent and that said Letters Patent are herebycorrected as shown below:

Column 3', line 35, "311 Corporation" should read 3M Corporation aColumn 5', line 11, "unitl'" should read until Signed and Scaled thisSeventeenth Day of May 1977 [SEAL] A nest:

RUTH C. MASON C. MARSHALL DANN Arresting Officer Commissioner uflaremsand Trademarks

1. A PRIMER ADAPTED TO INTIATING DETONATION OR NITROMETHANE BY STRONGSHOCK CONSISTING ESSENTIALLY OF THE COMBINATION OF AN OPEN-CELLEDPOLYMERIC FOAM HAVING DISPERED THEREIN FROM ABOUT 15 TO ABOUT 85 PERCENTBY WEIGHT OF HOLLOW THINWALLED MICROSPHERES CONTAINING ENTRAPPED AIRSAID FOAM BEING IN INTIMATE CONTACT WITH NITROMETHANE.
 2. Thecombination of claim 1 wherein said polymeric foam is polyurethanehaving a density of from about 0.02 to about 0.04 g/ml.
 3. Thecombination of claim 1 wherein said microspheres are ofphenol-formaldehyde, urea-formaldehyde, glass or ceramic.
 4. Thecombination of claim 3 wherein said microspheres are glass bubbles ofabout 20 to 100 microns and have a true particle density between 0.3 and0.4 g/cc.
 5. The combination of claim 1 wherein said microspheres aredispersed throughout the polymeric foam including the surface.
 6. Thecombination of claim 1 wherein said microspheres are embedded at thesurface of said polymeric foam.